This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. While local clusters are sufficient for small to medium size jobs, it is often necessary to deal with larger problems which require national and international resources such as the TeraGrid, Open Science Grid, or the PRAGMA grid. The Open Science Grid, a collection of community contributed resources, which are accessible using the Virtual Data Toolkit (VDT), represent a type of distributed resources which may be "shared when not in demand" by the owners. Such resources are shared by the formation of virtual organizations, which enable users with similar interests to share applications and compute resources.